TRP channels are a class of ion channels found on the plasma membrane of a variety of human (and other animal) cell types. There are at least 28 known human TRP channels which are broken into a number of families or groups based upon sequence homology and function. TRPA1 is a non-selective cation conducting channel that modulates membrane potential via flux of sodium, potassium and calcium. TRPA1 has been shown to be highly expressed in the human dorsal root ganglion neurons and peripheral sensory nerves. In humans, TRPA1 is activated by a number of reactive compounds such as acrolein, allylisothiocyanate, ozone as well as unreactive compounds such as nicotine and menthol and is thus thought to act as a ‘chemosensor.
Many of the known TRPA1 agonists are irritants that cause pain, irritation and neurogenic inflammation in humans and other animals. Therefore, it would be expected that TRPA1 antagonists or agents that block the biological effect of TRPA1 channel activators would be useful in the treatment of diseases such as asthma and its exacerbations, chronic cough and related maladies as well as being useful for the treatment of acute and chronic pain. Recently, it has also been shown that products of tissue damage and oxidative stress, e.g. 4-hydroxynonenal and related compounds, activate the TRPA1 channel. This finding provides additional rationale for the utility of small molecule TRPA1 antagonists in the treatment of diseases related to tissue damage, oxidative stress and bronchial smooth muscle contraction such as asthma, chronic obstructive pulmonary disease (COPD), occupational asthma, and virally-induced lung inflammation. Moreover, recently findings have correlated activation of TRPA1 channels with increased pain perception (Kosugi et al., J. Neurosci 27, (2007) 4443-4451; Kremayer et al., Neuron 66 (2010) 671-680; Wei et al., Pain 152 (2011) 582-591); Wei et al., Neurosci Lett 479 (2010) 253-256)) providing additional rationale for the utility of small molecule TRPA1 inhibitors in the treatment of pain disorders.